Abit PR5 Informations techniques télécharger pdf (Page 27)

In Pentium-based designs there is more than one

clock speed. The mainboard components run at one

speed and the CPU will run at the same speed in

its external activity, but will run at some multiple

of that speed internally.

External Clock

The External Clock, also sometimes referred to as

the external CPU clock or bus clock, is the CPU’ s

input clock. The CPU will interface with other com-

ponents at this speed and its internal clock speed is

a multiple of this external speed. The internal speed

is set by the Clock Multiplier Factor. For example,

the Intel Pentium P90, P120 and P150 CPUs all have

the same external clock, 60MHz, but have differ-

ent clock factors.

Internal Clock

The Internal Clock is a multiple of the external clock

and is the speed used to list the processor’ s operat-

ing speed. The internal speed is set by the Clock

Multiplier Factor. For example, the Intel Pentium

P150 CPU has a 150MHz internal clock speed, a

2.5 multiple of the 60MHz external clock.

Clock Multiplier Factor

The clock multiplier factor is the factor by which

the external clock is multiplied to set the CPU’ s

internal clock speed. The PR5 has four options: 1.5,

2, 2.5, 3. For example, the Pentium P166 requires a

66MHz external clock and a 2.5 clock multiplier

factor to establish its 166MHz internal clock speed.

Note: The full clock frequencies are rounded off

for convenience when listed, so while 66 x 2.5 =

165, the actual clock speed is 166MHz.

ISA Bus Clock

This is the clock speed of the ISA expansion bus

and may also be referred to as the ISA speed, AT

Bus Clock or AT clock. The original specification

was 8MHz. The slower speed ensures compatibil-

ity with all ISA expansion cards. Newer ISA ex-

pansion cards may be able to operate at faster

speeds, which provide increased performance. The

PR5 can be set for slower or faster ISA Bus clock

speeds. The slower speed ensures maximum com-

patibility.

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Abit PR5 Informations techniques Page 27

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